Stability and formability of complex oxides in M2O3–M′2O3 systems

Based on fundamental thermodynamics and a simple energy model for solid M2O3 oxides, two atomic parameters of their constituent elements are identified that govern the solid phase stability in an M2O3–M2′O3 binary system. They are P1=|rA−rB| and P2=(rA+rO)(rB+rO)(rA+rB+2rO), where, rA, rB and rO are the ionic radii of ion A, ion B and oxygen, respectively. Using 237 known M2O3–M2′O3 systems and these two parameters (P1 and P2), new rules were obtained not only on the formability of stable complex oxides but also on the conditions that these compounds being of MM′O3 stoichiometry and further of ABO3-type perovskite structure. The classification accuracy of such rules reaches respectively 98.7% for formability of complex oxides, 97.9% for the MM′O3 stoichiometry test, and 100% for the ABO3-type perovskite structure prediction. Thirty seven new systems are used to validate these empirical rules, and the prediction is in good agreement with experiment. The influence of ionic size difference on the phase stability is further discussed based on the proposed energy model. The new rules may help material scientists to practically predict new complex compounds as well as to further theoretically study phase stability in M2O3–M2′O3 systems.